1. Field of the Invention
The present invention relates to a method and apparatus for heating objects using microwave and far infrared radiation under reduced pressure for the purpose of drying, concentrating, defrosting, roasting or sterilizing the objects.
2. Description of the Prior Art
In prior art heaters which utilize microwave and far infrared radiation for drying, concentrating, defrosting, roasting or sterilizing objects, uniform heating is achieved by placing the objects in a chamber on jigs such as plates or trays and shelf-type support jig for supporting the jigs which is rotated or on a conveyor which is moved, or the objects are stirred.
However, prior art heaters having a rotatable jig for rotating objects to be heated are expensive and not suited for mass production due to the limited amount of objects that can be supported by the rotatable jig. Further, the scattering of powder and relatively light particles occurs in prior art heaters which stir objects to be dried, and because such heaters are complex and expensive, they are not preferred. Further, prior art heaters which move objects on a conveyor are quite suited for continuous production, but control of this type of heater is difficult. Namely, because objects are continuously supplied, a mixture of objects having different water contents is created, and because this makes it difficult to accurately detect the completion of heating, a high production efficiency can not be achieved. Further, because the accuracy in detecting the completion of heating is lowered, a control data base is required for each object when objects having different water contents are supplied at the time of each production, and this makes the control process extremely complicated. Furthermore, such heating apparatuses are large in scale, and this together with the lower level of accuracy requires much time and cost to obtain conforming articles. For the reasons given above, the use of heaters utilizing microwave and far infrared radiation under reduced pressure has not been widespread.